Conventional retaining walls are used to secure earth embankments against sliding and slumping. Retaining walls are made of various materials such as concrete, solid masonry, wood ties, bricks and blocks of stone and concrete. Typically, blocks are placed in rows overlaying on top of each other to form a wall. An example of such a system is shown in U.S. Pat. No. 4,914,876 to Forsberg, which shows each block having a decorative exterior face so that the wall presents an attractive appearance. For taller walls, a horizontal tie-back sheet must be located between lower layers of blocks, anchored to pins in the blocks, and extended rearwardly into an excavated area to be backfilled for retaining the lower portions of the wall against the outward force of the earth being retained. Because excavation is costly, and the tie-back sheet must extend rearward at least 2/3 of the wall height, this type of wall often is not cost effective. Also, where a single thickness of blocks must retain the earth, each block must be of appreciable size and weight, making handling for installation difficult. In addition, because different face textures are required for different applications, a variety of entirely different blocks must be fabricated and stocked.
To avoid the disadvantages of the heavy unitary blocks of Forsberg and the cost of the tie-back sheet, which requires substantial earthmoving and careful filling and grading of one layer at a time, walls systems having interlocking subcomponents have been employed.
Such a system is shown in U.S. Pat. No. 4,896,999 to Ruckstuhl. In this system, a frontal or face block is attached at its rear surface with a single connecting or anchoring block, or with blocks that may extend in lateral layers deep into the slope to anchor the wall. In such an arrangement, each layer that extends laterally into the slope is a substantially solid layer formed of blocks that do not easily slide apart. To provide adequate anchoring, such anchoring layers are spaced apart, with slope material backfilled between the layers. Each layer of backfill material must be carefully graded so that the anchoring layer installed on top of the backfill is substantially even, preventing vertical misalignments that may weaken or disengage the blocks.
Another concrete block wall system also using mechanical connections is shown in U.S. Pat. No. 4,884,378 to Scheiwiller. This system is used for freestanding walls and vertical retaining walls. No anchoring layers are provided because reinforced vertical beams are cast as part of the structure, with external blocks attached to the structure by dovetail joints. In Scheiwiller, the face blocks are attached to vertical columns. Therefore, sloped and sinuous wall structures may not be formed because such structures require that each succeeding layer be laterally offset in places relative to the layer on which it rests.
A further disadvantage of concrete block systems having mechanically attached blocks is that the individual blocks are weakened by the dovetail joints used, and may easily break. This is particularly a problem in blocks having a dovetail groove or slot that reduces the thickness of a planar block, such as shown in Scheiwiller.